Buggy code:
private ArrayList < WebSocketListener > listeners = new ArrayList < > ( ) ; private WebSocketClient webSocketService ; public void init ( ) { try { webSocketService = new WebSocketClient ( new URI ( Constants . SOCKET_SERVER ) ) { @ Override public void onOpen ( ServerHandshake handshakedata ) { Operation request = new Operation ( ) ; request . setUserId ( USER_ID ) ; request . setOperationType ( CONNECT ) ; request . setDeviceId ( DEVICE_ID ) ; sendRequest ( request ) ; for ( WebSocketListener listener : listeners ) { listener . OnOpened ( ) ; } } @ Override public void onMessage ( String message ) { System . out . println ( ( "Message<seq2seq4repair_space>arrived:<seq2seq4repair_space>" + message ) ) ; JSONParser = new Gson ( ) ; Track t ; TrackCriteria criteria ; Response response ; Operation request = JSONParser . fromJson ( message , Operation . class ) ; switch ( request . getOperationType ( ) ) { case OperationType . PAUSE : Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { mainBrowser . execute ( "PlayerController.pause();" ) ; } } ) ; break ; case OperationType . RESUME : break ; case OperationType . STOP : Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { mainBrowser . execute ( "PlayerController.stop();" ) ; } } ) ; break ; case OperationType . NEXT : Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { mainBrowser . execute ( "PlayerController.next();" ) ; } } ) ; break ; case OperationType . BACK : Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { mainBrowser . execute ( "PlayerController.back();" ) ; } } ) ; break ; case OperationType . PLAY : criteria = new TrackCriteria ( ) ; criteria . setId ( request . getId ( ) ) ; response = TrackController . getTrackById ( criteria ) ; Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { try { String JSON = response . getResponseBody ( ) ; mainBrowser . execute ( ( ( "PlayerController.play(JSON.stringify(" + JSON ) + "),<seq2seq4repair_space>false);" ) ) ; } catch ( IOException ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } } } ) ; break ; case OperationType . PLAY_FROM_PLAYLIST : criteria = new TrackCriteria ( ) ; criteria . setId ( request . getId ( ) ) ; response = TrackController . getTrackById ( criteria ) ; Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { try { String JSON = response . getResponseBody ( ) ; mainBrowser . execute ( ( ( "PlayerController.playSong(JSON.stringify(" + JSON ) + "),<seq2seq4repair_space>true);" ) ) ; } catch ( IOException ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } } } ) ; break ; case OperationType . REMOVE_FROM_PLAYLIST : criteria = new TrackCriteria ( ) ; criteria . setId ( request . getId ( ) ) ; response = TrackController . getTrackById ( criteria ) ; Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { try { String JSON = response . getResponseBody ( ) ; mainBrowser . execute ( ( ( "PlayerController.dequeueSong(JSON.stringify(" + JSON ) + "));" ) ) ; } catch ( IOException ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } } } ) ; break ; case OperationType . ENQUEUE : criteria = new TrackCriteria ( ) ; criteria . setId ( request . getId ( ) ) ; response = TrackController . getTrackById ( criteria ) ; Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { try { String JSON = response . getResponseBody ( ) ; mainBrowser . execute ( ( ( "PlayerController.enqueueSong(JSON.stringify(" + JSON ) + "));" ) ) ; } catch ( IOException ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } } } ) ; break ; case OperationType . VOLUME_DOWN : break ; case OperationType . VOLUME_UP : break ; case OperationType . SET_VOLUME : SessionConstants . VOLUME_FROM_USER = false ; Platform . runLater ( new Runnable ( ) { @ Override public void run ( ) { <START_BUG> mainBrowser . execute ( ( ( "PlayerController.setVolumeFromValue(" + ( request . getValue ( ) ) ) + ",<seq2seq4repair_space>false);" ) ) ; <END_BUG> } } ) ; case OperationType . SYNC : Operation syncRequest = new Operation ( ) ; request . setOperationType ( SYNC ) ; request . setUserId ( USER_ID ) ; sendRequest ( syncRequest ) ; } } @ Override public void onClose ( int code , String reason , boolean remote ) { System . out . println ( "WebSocket<seq2seq4repair_space>Closed<seq2seq4repair_space>..." ) ; } @ Override public void onError ( Exception ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } } ; } catch ( URISyntaxException ex ) { for ( WebSocketListener listener : listeners ) { listener . OnError ( ex . getMessage ( ) ) ; } } webSocketService . connect ( ) ; } public void addListener ( WebSocketListener listener ) { } public void removeListener ( WebSocketListener listener ) { } public void sendRequest ( Operation request ) { } public void sendRequest ( String operation ) { } public static void sendJSRequest ( Operation request ) { } public void closeConnection ( ) { } }

Fix:
mainBrowser . execute ( ( ( ( ( "OnVolumeChanged(" + ( ( request . getValue ( ) ) * 100 ) ) + ");<seq2seq4repair_space>PlayerController.setVolumeFromValue(" ) + ( request . getValue ( ) ) ) + ",<seq2seq4repair_space>false);" ) ) ;